Deep hole drill

ABSTRACT

A deep hole drill for chip-removing drilling in a workpiece includes a body which has a cutting head and an integral cutting part. The body defines a longitudinal axis of rotation and has a longitudinal internal channel which opens into an end face of the cutting head for receiving cuttings that are entrained in a cooling medium. A chip removing insert is disposed on the cutting head. A support pad and a guide bar are disposed on a generally cylindrical outer peripheral surface of the cutting head and are arranged in circumferentially spaced relationship to one another. Cooling ducts are formed in the outer peripheral surface and are oriented generally parallel to the axis. The cooling ducts are open at the end face for conducting cooling medium thereto. The cooling ducts are situated adjacent the support pad and guide bar, respectively, for cooling same.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a deep hole drill, which comprises acutter head as well as a connecting part integrated with the cutter headwhich part has a thread, said cutter head being equipped with a chipremoving cutting insert, at least one support pad as well as at leastone guide bar, the said cutter head has at least one opening fordischarging chips, said opening transforming into an inner channel ofthe cutter head. The two most common systems in deep hole drilling arepresently the STS (Single Tube System) system and the Ejector system,the present invention relates to both these systems.

PRIOR ART

In deep hole drilling, in a workpiece a commonly occurring problem isthat the support pads and guide bars, which are arranged on the cutterhead, are subjected to the formation of crack, during the deep holedrilling. The reason for this is that the support pads/guide bars arenormally made of solid cemented carbide, whereby said support pads/guidebars may be exchangeably fixed on the cutter head or in various waysconnected by soldering to the cutter head. During the drilling process,the support pads/guide bars are exposed to high temperatures by the factthat the friction against the hole wall may be high. However, most oftenthe entire support pad/guide bar does not abut against the hole wall,and therefore only a part of said support pad/guide bar is exposed tosaid friction. The cooling liquid flowing between the cutter head andthe bore hole will not be in contact with the support pad/guide bar inthose areas where abutment takes place between the support pad/guide barand the hole wall to a sufficient extent. As a consequence of theseinteracting circumstances. i.e. high friction and deficient cooling,cracks arise in the support pads/guide bars, which reduce the servicelife of said support pads/guide bars.

AIMS AND FEATURES OF THE INVENTION

The present invention has as its aim the definition of a deep hole drillof the kind mentioned in the introduction, where the cooling liquid isgiven a greater possibility to provide cooling of the support pad/guidebar, in an efficient way, during drilling.

Yet another aim of the invention is to improve the chip removal, whichreduces the risk for chips being stuck between the support pad/guide barand the hole wall, which additionally may reduce the service life ofsaid support pads/guide bars.

The aims of the present invention are realized by means of a deep holedrill for chip-removing drilling in a workpiece. The drill comprises abody which includes a cutting head and an integral connecting partadapted for connection to a drill tube. The body forms a longitudinalaxis of rotation and has a longitudinal internal channel opening into anend face of the cutting head for receiving cuttings that are entrainedin a cooling medium. A chip-removing insert is disposed on the cuttinghead. A support pad is disposed on a generally cylindrical outerperipheral surface of the cutting head. A guide bar is disposed on theouter peripheral surface in circumferentially spaced relationship to thesupport pad. A cooling duct is formed in the outer peripheral surfaceand is oriented generally parallel to the axis at a location adjacent tothe support pad. The cooling duct opens at the end face for conductingcooling medium toward the end face. The cooling duct is situatedadjacent the support pad for cooling the support pad.

BRIEF DESCRIPTION OF THE DRAWINGS

Below an embodiment of the invention will be described, reference beingmade to the accompanying drawings, where

FIG. 1 shows a front view of a deep hole drill according to prior art;

FIG. 2 shows a front view of an embodiment of a deep hole drillaccording to the present invention;

FIG. 3 shows a perspective view obliquely from below of the deep holedrill according to FIG. 2;

FIG. 4 shows a perspective view obliquely from above of the deep holedrill according to FIG. 2;

FIG. 5 shows a front view of the deep hole drill according to FIG. 2,where the resultant of the cutting forces as well as the forces actingon the support pad and the guide bars are indicated;

FIG. 6 shows schematically the surface, which lets through coolingliquid on a deep hole drill according to prior art;

FIG. 7 shows schematically the surface which lets through cooling liquidon a deep hole drill according to the present invention; and

FIG. 8 shows a perspective view of an alternative embodiment of a deephole drill according to the present invention.

DESCRIPTION OF PRIOR ART

First embodiment of a deep hole drill according to the presentinvention:

The deep hole drill A according to the prior art illustrated in FIG. 1is provided with a support pad B and a guide bar C. In that connection,no special arrangements are taken to overcome the problems which havebeen discussed above under the heading Prior art, i.e. that the supportpad B and the guide bar C are subject to crack formation.

The deep hole drill according to the present invention illustrated inFIGS. 2-5 comprises a cutter head 1 as well as a connecting part 3integrated with the cutter head 1, which connecting part is providedwith an external thread 5. The connecting part 3 is connected to a drilltube (not shown), via said external thread 5, which in turn is carriedby a suitable supporting device.

The cutter head 1 is, in the usual way, equipped with cutting inserts 7,these however not being described in detail since they do not constitutea part of the present invention. Furthermore, the cutter head 1 isprovided with a support pad 9 and a guide bar 10, which in theembodiment illustrated consist of exchangeable units according to theprinciple of indexable inserts. As is most clearly seen in FIG. 3, thesupport pad 9 and the guide bar 10 are provided with a chamfers 11 and12, respectively, at the end thereof turned towards the connecting partIn that connection, the chamfers 11, 12 are so formed that theirabutment against the cutter head 1 takes place without there being anydifference in level between the chamfers 11, 12 and the portions of thecutter head I which said chamfers 11, 12 abut against.

The cutter head 1 of the deep hole drill according to the presentinvention is also provided with a first cooling duct 13 and a secondcooling duct 14, the first cooling duct 13 being situated adjacent tothe support pad 9 while the second cooling duct 14 being situatedadjacent to the guide bar 10. Said cooling ducts 13, 14 extend in theaxial direction of the deep hole drill and are preferably parallel tothe axial direction of the deep hole drill. In the embodimentillustrated, the cooling ducts 13, 14 are formed as concave countersinksin the cutter head 1, the cooling ducts having, when seen incross-section, a softly rounded bottom with a certain radius ofcurvature.

The cutter head 1 is provided, in the usual way, with an inner channelfor discharging the chips produced during the rotation of the cutterhead 1 in relation to the workpiece. In that connection, the cutter head1 is provided with a first opening 15, through which the majority of thechips produced are discharged, said first opening 15 being connected tothe interior channel of the cutter head 1. The cutter head 1 has also asecond opening 16, which also is used to discharge chips, said secondopening 16 also being in connection with the interior channel. In theillustrated embodiment, the first opening 15 is somewhat larger than thesecond opening 16.

The function of the deep hole drill according to the invention:

In conjunction with a hole being drilled in a work-piece, the workpieceis clamped in a kind of fixture while the deep hole drill with the drilltube thereof is clamped in a rotatable chuck, and then the workpiece andthe deep hole drill are pressed up against each other. The deep holedrill with the drill tube thereof is then brought to rotate and isdisplaced axially in relation to the workpiece, a hole being drilled insaid workpiece. During the drilling process, the support pad 9 and theguide bar 10 abut against the hole wall, whereby a temperature risetakes place in the support pad 9 and the guide bar 10 by virtue of thefriction against the hole wall. In this connection, reference is made toFIG. 5 which, on one hand, shows the resultant R of the radial cuttingforces exerted by the cutting inserts 7 and, on the other hand, theforces acting from the hole wall on the support pad 9 and the guide bar10 which compensate said resultant R. Then, it should be noted thatforce F1 acting on the support pad 9 is larger than the force F2 actingon the guide bar 10. As a result of this force distribution, the supportpad 9 is exposed to a larger friction and thereby also a greatertemperature rise.

In order to compensate for said temperature rise, cooling medium,commonly oil, is supplied into the space between the drill tube of thedeep hole drill and the hole wall when an STS system is concerned, saidcooling medium being brought to flow in the direction towards the cutterhead 1. When the cooling medium reaches the cutter head 1, anaccumulation of cooling medium takes place in the first and secondcooling duct 13 and 14, respectively, the main part of the coolingmedium flowing to the free chip removing end of the cutter head I viathe first and second cooling ducts 13 and 14, respectively. Since thecutter head I rotates in the direction of the arrow S, see FIG. 5, i.e.the support pad 9 is to be found behind the first cooling duct 13 in thedirection of rotation, said support pad 9 will pass through theaccumulation of cooling medium which is generated by the first coolingduct 13. Thereby, a significantly improved cooling of the support pad 9is achieved in comparison with the cooling which is obtained for a deephole drill according to prior art.

It is true that a corresponding cooling of the guide bar 10 is notobtained, but an equally satisfactory cooling of the guide bar 10 is notrequired since the same it is exposed to a force F2 from the hole wallwhich is significantly smaller than the force F1 which the support pad 9is exposed to.

In FIGS. 6 and 7, the difference in volume of cooling medium reachingthe chip removing end of the cutter head 1 is schematically illustratedfor a deep hole drill according to prior art, FIG. 6, and for a deephole drill according to the present invention, FIG. 7. The space G (FIG.6) or G′ (FIG. 7) available for the cooling medium to flow forward in.For a deep hole drill according to prior art, see FIG. 6, the availablespace G is approximately 12% of the cross-section area of the drilledhole, while for a deep hole drill according to the present invention,see FIG. 7, the available space G for the cooling medium isapproximately 15% of that cross-sectional area. This equals an increaseof 20% when comparing deep hole drill according to prior art and a deephole drill according to the present invention.

The increased volume of cooling medium which reaches the chip removingend of the cutter head 1 is, naturally, positive for the chip removalsince the cooling medium turns at the chip removing end and pulls thechips with it through the first opening 15 and the second opening 16.The fact that the second cooling duct 14 is situated quite in front ofthe first opening 15. seen in the direction of rotation S, see FIG. 5,of the cutter head 1, ensures that an accumulated volume of coolingmedium can turn back and flow through the first opening 15, saidaccumulated volume of cooling medium in an efficient way pulling chipswith it from the chip removing end of the cutter head 1. The coolingmedium then continues in the interior channel of the deep hole drill andfurther inside in the appurtenant drill tube (not shown).

Alternative embodiment of a deep hole drill of the present invention:

The deep hole drill illustrated in FIG. 8 comprises, like the embodimentaccording to FIGS. 3-5, a cutter head 1′ as well as a fastening part 3,which in principle is identical with the fastening part 3 of theembodiment illustrated in FIGS. 3-5. The design of the cutter head 1′ iswhat distinguishes the deep hole drill according to FIG. 8 from the deephole drill according to FIGS. 3-5, and more precisely the arrangement ofan additional cooling duct 17′, i.e. a third cooling duct, which issituated besides and quite close to the guide bar 10, i.e., in directproximity thereto. Thus, the deep hole drill according to FIG. 8 isprovided with a first and a second cooling medium duct 13 and 14,respectively, which is seen in FIG. 8. If the same direction of rotationis valid for the deep hole drill according to FIG. 8 as the deep holedrill according to FIGS. 3-5, see arrow S in FIG. 5, the third coolingduct 17′ is positioned in front of the guide bar 10 in said direction ofrotation S. Said third cooling duct 17′ should guarantee that the guidebar 10 receives a satisfactory cooling/lubrication by the cooling mediumflowing in the third cooling duct 17′. Normally, the third cooling duct17′ has smaller dimensions than the first and second cooling ducts 13and 14.

FEASIBLE MODIFICATIONS OF THE INVENTION

In the embodiment described above, two cooling ducts 13, 14 are arrangedon the circumference of the cutter head 1. However, within the scope ofthe invention, it is feasible that only one cooling duct is arranged onthe circumference of the cutter head 1, the cooling duct 13 which isarranged adjacent to the support pad 9, in that case, being preferable.The reason for this is seen in the description above when the cooling ofthe support pad 9 is discussed.

In the embodiment described above, the two cooling ducts 13, 14 areshown having in the main the same flow cross-section in FIG. 2. However,within the scope of the present invention, it is conceivable that, forinstance, the second cooling duct 14 has a larger flow cross-sectionthan the first cooling duct 13 since said second cooling duct 14 shouldserve two cutting inserts, i.e. let cooling medium pass which dischargeschips from two cutting inserts.

In the embodiment described above, the support pad 7 and the guide bar 9are in the form of exchangeable units according to the principle ofindexable inserts. However, within the scope of the invention, it isfeasible that the support pad/guide bar is connected by soldering to thecutter head I of the deep hole drill.

In the description above of the function of the deep hole drillaccording to the invention, it has been assumed that the so-called STSsystem is used. However, a deep hole drill according to the presentinvention may also be used, which has been pointed out in theintroduction of this patent application, in, for instance, the so calledEjector system or other existing systems for deep hole drilling. In theEjector system, double drill tubes are used, approximately half of thecooling medium turning around before it reaches the chip removing end ofthe cutter head I and thereby providing an Ejector effect whichactivates the cooling medium reaching the chip removing end andtransports chips with it on its way from the chip removing end.

In the above description of the function of the deep hole drillaccording to the invention, the deep hole drill is rotated while theworkpiece is not rotated. However, it is also feasible, within the scopeof the invention, that the workpiece rotates while the deep hole drilldo not rotate but only is axially displaced in relation to theworkpiece. According to an additional variant, it is conceivable thatboth the deep hole drill and the workpiece rotate in oppositedirections.

Thus, regardless of whether the drill is rotated relative to astationary workpiece, or the workpiece is rotated relative to astationary drill, or the drill and the workpiece are both rotated inopposite directions, the cooling duct 13 will be disposed on a side ofthe support pad facing the direction of rotary cutting, that is, facingin the same direction as the cutting inserts (i.e., facing in directionS in FIG. 5).

Reference being made to FIG. 7, it should be pointed out that the spaceG′ other than the cooling ducts 13, 14 could be blocked, e.g., by fiberstrips or the like, applied on the outside of the cutter head. By suchan arrangement, the cooling medium is forced to flow only in saidcooling ducts, at which an additionally improved cooling of the supportpad/guide bar may be counted upon.

What is claimed is:
 1. A deep hole drill for chip-removing drilling in aworkpiece comprising: a body including a cutting head and an integralconnecting part adapted for connection to a drill tube, the bodydefining a longitudinal axis of rotation and having a longitudinalinternal channel opening into an end face of the cutting head forreceiving and conducting cuttings entrained in a cooling medium; achip-removing insert disposed on the cutting head; a support paddisposed on a generally cylindrical outer peripheral surface of thecutting head; and a guide bar disposed on the outer peripheral surfacein circumferentially spaced relationship to the support pad; wherein afirst cooling duct having a first cross-sectional area is formed in theouter peripheral surface and oriented generally parallel to the axis,the first cooling duct opening at the end face for conducting coolingmedium toward the end face and is situated adjacent the support pad forcooling the support pad, and a second cooling duct having a secondcross-sectional area is formed in the outer peripheral surface incircumferentially spaced relationship to the first cooling duct, thesecond cooling duct oriented generally parallel to the axis and openingat the end face for conducting cooling medium thereto, wherein the firstand second cross-sectional areas are different from each other.
 2. Thedeep hole drill according to claim 1 wherein the cutting insert faces adirection of rotary cutting, the cooling duct arranged on a side of thesupport pad facing in the direction of rotary cutting.
 3. The deep holedrill according to claim 2 wherein the second cooling duct is arrangedadjacent to the guide bar.
 4. The deep hole drill according to claim 3wherein the second cooling duct is arranged near a side of the guide barfacing opposite the direction of rotary cutting.
 5. The deep hole drillaccording to claim 1 wherein the second cooling duct has a largercross-sectional area than the first cooling duct.
 6. The deep hole drillaccording to claim 1 wherein at least one of said first and secondcooling ducts comprises a concave countersink formed in the outerperipheral surface, the countersink having a radiused bottom.
 7. Thedeep hole drill according to claim 1 wherein the body is provided withan additional cooling duct in direct proximity to the guide bar.
 8. Thedeep hole drill according to claim 7 wherein the additional cooling ductis arranged at a side of the guide bar facing in the direction of rotarycutting.